I. Field of the Invention
The present invention concerns rotary viscometry with a low heat-transmissible spindle, as well as the spindle and associated viscometer apparatus with the spindle included therewith.
II. Prior Art and Problems
Standard test method ASTM D 2983 for low-temperature viscosity of automotive fluid lubricants measured by Brookfield viscometer determines the low-shear-rate viscosity in the temperature range from -5 to -40 degrees C. The fluid viscosity, of course, is temperature-dependent, and certain ways and means have been introduced and disclosed to assist in controlling the temperature so as to provide more reliable data. See, e.g., ASTM D 2983-87 (Reapproved 1993) and Selby, U.S. Pat. Nos. 5,526,681 and 5,587,522, which are incorporated herein by reference.
A concern for possible heat-transfer losses through the metal spindle led Theodore W. Selby to develop a spindle having a shaft bisected into upper and lower metal components and tied together by a phenolic composite sleeve. That spindle was an attempt to control a problem of transfer of heat, and it has been used since 1958. As noted by Mr. Selby in abandoned U.S. patent application Ser. No. 08/490,111, several drawbacks attend this bisected-shaft approach:
1) The spindle shaft, being separated into three parts, is subject to imbalance and undesirable, accidental disassembly. PA1 2) The phenolic composite insulator portion of the three-part shaft is typically of a larger diameter than the metal rod portion, commonly twice or more that of the metal spindle portion, and extends for a significant distance along the axis of rotation, commonly an inch. PA1 3) The large insulator portion requires an upper closure to the stator having a larger opening to accommodate the insulator passing through. This engenders the introduction of ambient air into the stator and test fluid, causing an unwanted rise in the temperature of the test fluid, which disturbs the accuracy of the measurement. PA1 4) Manufacture of this item is more involved than desired.
With amelioration of the same concern in mind, Mr. Selby invented a heat-dissipating viscometer rotor comprising an elongate member distributed along an axis of rotation having opposing attachment and sample-immersion ends, and a protuberance (which can be a set of fins) therebetween, all the same typically made from stainless steel, which was set forth in the abandoned '111 application.
Unfortunately, data obtained by the aforementioned ASTM protocol even as improved so well by the disclosures of the Selby patents can be less accurate than desired in today's world of high precision lubricant technology. Furthermore, as noted, data obtained with the buffered-shaft spindle was not highly accurate, and the finned rotor did not dissipate enough heat.
It would be desirable to ameliorate the problems remaining.